The eye exam chart is a chart used to subjectively measure visual acuity. It is most commonly known as the Snellen chart, which usually shows 11 rows of capital letters. This eye test can only be considered a screening test, as a variety of factors, such as lighting, glare, and monitor quality, can affect the results. Health professionals, such as optometrists, doctors, or nurses, often use eye charts to evaluate people for vision problems.
Ophthalmologists, doctors who specialize in the eye, also use eye charts to monitor their patients' visual acuity in response to various therapies. To assess near vision, the ophthalmologist may use a small portable card called a Jaeger eye chart. The Jaeger graphic consists of short blocks of text in various font sizes. For this test, the child sits in a chair 10 feet away from the board, gently holding an eye mask over one eye. If you don't wear glasses or contact lenses, your ophthalmologist will use the results to see if you need them. A thorough eye exam can often detect certain underlying diseases that may endanger vision and eye health, such as diabetes, high blood pressure, high cholesterol, tumors, autoimmune diseases, and thyroid disorders.
Before the Snellen eye chart was developed in the 1860s by Dutch ophthalmologist Hermann Snellen, each ophthalmologist had their own chart that they preferred to use. This standardized ophthalmic chart allowed a person to provide a standardized prescription from any eye care provider who chose any eyeglass manufacturer and obtain the same optical lenses to accurately correct their vision. In the United States, the standard eye chart location is on a wall that is 20 feet away from the eyes. During an eye exam, the ophthalmologist will ask you to look for the smallest line of letters you can read and then ask you to read it. Even Japanese ophthalmologist Ema Tenko, who studied with Snellen, created an eye chart that was used in Japan.
Parents and caregivers can examine their child's eyesight from home to identify possible vision problems that require an eye professional. Eye professionals can use certain tables to measure distance vision and others to measure near vision. The font size on a modern Jaeger eye chart generally ranges from J10 (approximately 14 points in Times New Roman font) to J1 (approximately 3 points in Times New Roman). Optotype is still the most common test for evaluating standard vision. Although eye chart tests identify refractive errors, they cannot detect signs of deficiencies in visual abilities or diseases such as glaucoma, cataracts, or macular degeneration. For this reason, it is important to visit an ophthalmologist for a comprehensive eye exam if you have any concerns about your vision.
